Deep volcanic morphology below Lanzarote, Canaries, from gravity inversion: New results for Timanfaya and implications

Abstract

The deep roots of oceanic island volcanoes are poorly known and geophysical models can help to constrain processes such as magma storage and transport before and during eruptions. Lanzarote, Canary Islands, is a volcanic island in post-erosional phase where, in the 18th century, one of the most important historical eruptions, considering duration and volume, of the Canary Islands took place in the Timanfaya area. To improve the knowledge on the structure of Lanzarote and in Timanfaya area, we carry out a gravity determination of the subsurface anomalous 3D density structure, using an improved quasi-automatic inversion methodology. The obtained model presents a 3D morphology of anomalous density bodies. We describe the improvements of the inversion methodology, the adjusted model and interpretative conclusions corresponding to the structure and the long-term cumulative magmatic plumbing system of the island. Three high-density sources are described as resulting in the inference of three main volcanic complexes: a large central complex (San Bartolomé) and two smaller complexes, one in the NE and a third smaller one located in the SW close to the Timanfaya area. The outcrops of Miocene lava flows from the center of the Island can be attributed to the top of the central intrusive model. We infer the local plumbing system for Timanfaya volcano area by means of strongly tilted successive branches of magma departing from the SW intrusive body. The structural results show no evidence of any magma chamber below Timanfaya as proposed by previous works. We also present a comparison of the gravity results and geological observations, showing different cases of correlation in the Island. They go from a good match between the gravity anomaly and the position of the central volcanic structure, to no anomaly associated to the fissural Quaternary volcanic activity.